Drilling subterranean wells for oil and gas is expensive and time consuming. Formations containing oil and gas are typically located thousands of feet below the earth's surface. To access the oil and gas, very long lengths of drill pipe can be required. Further, multiple wellbores can be drilled in close proximity to each other and can be directed to predetermined underground targets in a process known as “directional drilling” in which the wellbore(s) deviate from vertical at some point along their length. Accurate surveys of directional wellbores are needed to correctly locate each wellbore in order to avoid intersecting existing wells. Survey data can include the inclination (deviation from vertical) and azimuth (orientation from north) of multiple points along a wellbore.
FIG. 4 illustrates a surface and a sectional subsurface view of a wellbore 400 through the sub-surface 401 and corresponding drilling platform 402 located on the surface 403. The wellbore 400 extends below the drilling platform 402 and slants towards an orientation ending at drill location 404. Inclination is shown measured at two points, point A 405 and drill location 406. Inclination at point A 407 is the angle between the tangent of the curve of the wellbore at point A 406 and vertical 408. Inclination at the drill location 409 is also shown. Inclination is calculated through the gravity environment, usually using one or more accelerometers. Azimuth 410, the angle between the orientation of the wellbore path 411 and north 412, is often calculated using both the inclination and the magnetic or rotational environment. The combination of inclination and azimuth is referred to as attitude.
Current methods of surveying a wellbore require that drilling be stopped so that the sensors in a bottom hole assembly (BHA) of a drill string can be stationary in order to get accurate measurements. As such, survey data has been collected when drilling stops in order to add new sections of drill pipe. This operation typically occurs only once for every 90 feet of drill string length. Collecting survey data at stage in drilling can be a limitation preventing the drilling operation from resuming. If additional survey data is to be collected, the drilling must again stop, adding to the overall time required to complete a drilling operation. Accordingly, new methods are needed in the industry to provide accurate and timely survey data.